What a molar pregnancy is

The NHS defines it as "when there's a problem with a fertilised egg, which means a baby and a placenta do not develop the way they should after conception. A molar pregnancy will not be able to survive. It happens by chance and is rare."

The Charing Cross Gestational Trophoblast Disease Service, which runs one of the UK's national follow-up centres, explains the mechanism: at conception "the fertilised cell becomes abnormal as a result of an imbalance in the number of chromosomes supplied from the mother and the father. The molar pregnancy cells that result can grow quickly, produce hCG... and so give a positive pregnancy test but are unable to form a proper embryo."

The NHS describes the two types. In a complete molar pregnancy, abnormal cells grow in the womb and there is no sign of a baby. In a partial molar pregnancy, there may be early signs of a baby, but it cannot fully develop or survive. The medical name for both is a hydatidiform mole.

The NHS is unambiguous about cause: "A molar pregnancy happens by chance. It's not caused by either parent doing something wrong." It lists being a young teenager or over 45, having had a molar pregnancy before, and having an Asian background as factors that make it more likely.

How it is usually found

Often, it is found after the fact. Miscarriage UK, formerly the Miscarriage Association, notes that "most cases of molar pregnancy are diagnosed after what appears to be a 'normal' miscarriage where the woman has had surgical management of her miscarriage" — the tissue is sent for laboratory examination, and that is what identifies it. There can be a gap of days or weeks between the miscarriage and being told.

The NHS says a molar pregnancy may also be picked up at the first ultrasound scan at around 8 to 14 weeks, and that it may cause no symptoms at all, or only ordinary pregnancy symptoms.

The NHS says to contact a midwife or GP urgently if you are pregnant and you have:

any bleeding or dark discharge from your vagina
severe sickness — feeling or being sick often
a bump that looks bigger than it should for your stage of pregnancy
any other symptoms you are worried about

Miscarriage UK explains why several of those cluster together: most of the symptoms are caused by very high hCG levels, which is also why they can look like an exaggerated version of ordinary pregnancy.

The tests the NHS lists are a blood test for hCG, which is usually higher than normal, an ultrasound scan, and an appointment with a gynaecologist or at an early pregnancy assessment unit.

Treatment

The NHS is direct: a molar pregnancy will not be able to survive. It may end on its own as a miscarriage. If it does not, "it's usually treated with a procedure to remove the pregnancy", generally under general anaesthetic, and sometimes medicine can be used instead.

Miscarriage UK adds a point that matters to a lot of people emotionally: "This process is not a termination of pregnancy (an abortion). In most cases there never was an embryo or it died at a very early stage, and even in a partial mole it will not develop. Even so, you may still feel a sense of loss for what would have been your baby."

Detailed clinical management in the UK follows the RCOG's Green-top Guideline No. 38 on gestational trophoblastic disease, which also sets out how cases are registered with the national screening centres.

What the hCG follow-up is for

This is the part that makes molar pregnancy different from other early losses, and the part worth understanding properly.

The NHS explains that after treatment "you'll have regular blood and urine tests to check your hCG hormone level is returning to normal", and why: "Very rarely, molar pregnancy cells can remain in the womb and become cancerous... This is called an invasive mole or choriocarcinoma. If this happens, it can usually be successfully treated with chemotherapy."

Miscarriage UK puts the reassurance alongside the risk: "If you have a hydatidiform mole that has gone without needing chemotherapy, then you do not have cancer. A very small proportion of molar pregnancies can develop into an invasive mole or choriocarcinoma, which is a form of cancer. Fortunately it is a cancer with an almost 100% cure rate."

Charing Cross describes the same spectrum from the clinical side: gestational trophoblastic disease ranges from the usually benign partial mole through complete mole and invasive mole to choriocarcinoma, and it notes that where further treatment is needed after surgery, chemotherapy "is curative for nearly all patients".

Follow-up is run through specialist centres, and samples are sent to them rather than handled locally. How long it lasts depends on the type of mole and on how your hCG behaves — your centre will tell you, and the interval is not something to estimate from a website.

Contraception and trying again

The NHS advises using contraception while you are getting follow-up care, and says: "Having a molar pregnancy does not affect your chances of getting pregnant again. But it's important to wait until your doctor tells you it's safe before you start trying for a baby."

Miscarriage UK explains the reason for the wait, which is not arbitrary: "A new pregnancy could mask the regrowth of molar cells and make them very difficult to detect and treat."

On recurrence, Miscarriage UK gives the figures as roughly one in 600 for molar pregnancy in general, around one in 100 after one mole, and around one in 7.5 after two — adding that "there is an excellent chance that you will have a perfectly normal pregnancy next time."

Where to get support

Miscarriage UK has a molar pregnancy section, a staffed support line and a monthly online support group specifically for people affected by molar pregnancy. Tommy's has a molar pregnancy information and support section. The Charing Cross service publishes patient leaflets and answers questions about follow-up. The HSE's molar pregnancy page covers the equivalent Irish pathway.

Two things are commonly said to people after a molar pregnancy that are not true and are worth refusing: that it "wasn't a real pregnancy", and that because it was rare there is nothing to grieve. Neither follows.

Molar Pregnancy